Pressure control valve

1. A pressure control valve comprising: a valve main body provided with a valve chamber having a valve seat portion which a rod-shaped valve body moves close to and away from, an inflow port, and an outflow port; and a pressure response element having a diaphragm defining an upper surface of said valve chamber and driving said valve body in an opening and closing direction, and a lid-like member defining a sealed pressure chamber in cooperation with said diaphragm, wherein an inert gas having a thermal expansion coefficient equal to or less than a predetermined value is enclosed within said sealed pressure chamber, and an internal volume of said sealed pressure chamber is set such that said valve body comes to a full-open state in the case that the pressure of said valve chamber becomes a predetermined pressure or more higher than the pressure at which said valve body starts opening; and wherein the internal volume of said sealed pressure chamber is set such that a ratio Vmin/Vmax becomes equal to or less than 0.7, where Vmax denotes an internal volume of said sealed pressure chamber at a time when said valve body is in a full-close state, and Vmin denotes an internal volume of said sealed pressure chamber at a time when said valve body is in a full-open state; and wherein a connection hole is formed in said diaphragm, and an upper end portion of said valve body is bonded to said diaphragm, said valve body being provided with a vertical hole with an upper surface opening, and said vertical hole with an upper surface opening being in alignment with said connection hole whereby said sealed pressure chamber and said vertical hole are in communication through said connection hole to expand said sealed pressure chamber.

2. A pressure control valve as claimed in claim 1 , wherein a single gas or a mixed gas is used as said inert gas.

3. A pressure control valve as claimed in claim 2 , wherein said single gas is nitrogen or helium.